It has become increasingly important to provide accurate measurements of various parameters such as pressure. One area in which such measurement of pressure is important is the intake manifold pressure which represents an engine fuel demand parameter as shown in the U.S. patent application Ser. No. 881,321 entitled Microprocessor Based Electronic Engine Control System, filed Sept. 27, 1977 and having the same assignee as the subject application.
In the manufacture of a large number of capacitors, it is extremely difficult to control all of the parameters with sufficient accuracy to obtain the required capacitance value for each capacitor manufactured. This is particularly true when high precision capacitors are required. As a result, it is either necessary to discard large numbers of capacitors because they do not meet the specified tolerances or to trim the capacitors to value.
The U.S. Patent to Lumley No. 3,597,579 shows a laser trimming technique for capacitors involving adjusting the effective area of an electrode by applying radiant energy to the electrode. An electrical potential is applied across the electrodes of the capacitor while the radiant energy is applied thereto to inhibit the formation of electrical shorts.
The trimming of a pressure-sensing capacitor is complicated by the fact that the capacitance value of the capacitor varies with pressure. Therefore, any trimming of pressure-sensing capacitors must allow for reproducible sensor performance through a range of pressures to eliminate or substantially reduce the need for complete calibration of individual sensors.
The U.S. Patent to Brown, No. 3,750,476, issued Aug. 7, 1974, discloses a pressure transducer comprising a pair of sealed members uniformly spaced and coated with an electrically conductive material to define a pair of plates in a capacitor. The U.S. Patent to Polye, No. 3,858,097, issued Dec. 13, l974, discloses a pressure sensing capacitor comprising a hollow body having spaced opposite walls supported at their edges with electrical conducting means formed on deflecting portions of the wall. Other capacitor pressure transducers are shown in U.S. Pat. Nos. 3,634,727, 3,715,638 and 3,753,373.
Filed concurrently herewith is a patent application identified as P-314 by Binneg Yanbing Lao entitled "Improved Pressure Sensing Capacitor and Method of Trimming Same" and having a common assignee as the subject application. The Lao application discloses a pressure-sensing capacitor and method wherein an eccentric disc portion is trimmed from the capacitor's electrode.